[FFmpeg-devel] [PATCH 1 of 1] movenc: enable writing of interlace information back to the 'fiel' atom. (3rd Version)
Michael Niedermayer
michaelni at gmx.at
Mon Nov 5 16:05:01 CET 2012
On Fri, Nov 02, 2012 at 01:15:11PM +0000, Tim Nicholson wrote:
> On 01/11/12 22:01, Michael Niedermayer wrote:
> > On Thu, Nov 01, 2012 at 03:31:42PM +0000, Tim Nicholson wrote:
> >> On 01/11/12 14:53, Michael Niedermayer wrote:
> >>> [..]
> >>>
> >>> This does not look safe.
> >>> the encoder (that can run in a seperate thread) can free or change the
> >>> coded_frame. Even if it zeros the pointer before freeing above is
> >>> not atomic, the pointer is checked to be not NULL then loaded into
> >>> a register and then top_field_first read based on this pointer.
> >>> if the data is freed between these it can crash or produce undefined
> >>> behavior.
> >>>
> >>
> >> From what I could see the data is only freed within the *close function
> >> of the encoder, but not during the *encode2 function. As the close
> >> function(s) are called after the the output file(s) are flushed and
> >> closed in the main ffmpeg transcode() function, I thought this would be
> >> safe.
> >
> > does it work with applications other than ffmpeg itself ?
> > also consider some application might use libavformat without a
> > libavcodec based encoder. And muxers should have this information
> > at their disposal if they need it before the first frame is submited
> > to the encoder so it can be put in a header that is sent as early as
> > possible.
> >
> >
> >> If this is not the case then afaik the *only* safe thing is to set
> >> the flag in the encoder encode function, but this will happen every
> >> frame which feels OTT! (but would keep the code self contained) I am
> >> happy to do it this way if it is acceptable.
> >
> > Would it be possible for the user application to set this information
> > correctly before writing the file header ?
> > That is that the muxer would then just read it out of AVCodecContext
> > ?
> >
> > [...]
> >
>
> Attached a new version that works within ffmpeg when it is setting up
> the other interlace flags the muxer then works as described above..
>
> I have followed the current logic that in the absence of user
> intervention use the input settings, so that the value of
> enc->field_order is in sync with big_picture.interlaced_frame &
> big_picture.top_field_first. It could be argued that in the absence of
> specific user setting of interlaced flags (ildct etc) the output should
> be flagged as progressive, but in that case both sets of flags should be
> forced to progressive to keep them in sync.
>
> As there have been reports of FCP assuming material is interlaced unless
> the fiel atom says otherwise, I have made sure that the flag is set one
> way or the other and not left undefined.
>
> Updated fate checksums included.
>
>
> --
> Tim
>
>
> ffmpeg.c | 12 ++++++++++++
> tests/ref/fate/vsynth1-prores | 4 ++--
> tests/ref/fate/vsynth1-prores_kostya | 4 ++--
> tests/ref/fate/vsynth1-qtrle | 4 ++--
> tests/ref/fate/vsynth1-qtrlegray | 4 ++--
> tests/ref/fate/vsynth1-svq1 | 4 ++--
> tests/ref/fate/vsynth2-prores | 4 ++--
> tests/ref/fate/vsynth2-prores_kostya | 4 ++--
> tests/ref/fate/vsynth2-qtrle | 4 ++--
> tests/ref/fate/vsynth2-qtrlegray | 4 ++--
> tests/ref/fate/vsynth2-svq1 | 4 ++--
> 11 files changed, 32 insertions(+), 20 deletions(-)
> 98d67c2cbee74ef5df129869ebdbc3ed5cb29403 0001-ffmpeg-add-setting-of-field_order-flag.patch
> From 57d13331b1d12055f674f13b670eab09577608c5 Mon Sep 17 00:00:00 2001
> From: Tim Nicholson <Tim.Nicholson at bbc.co.uk>
> Date: Fri, 2 Nov 2012 13:09:48 +0000
> Subject: [PATCH] ffmpeg: add setting of field_order flag
>
> ---
> ffmpeg.c | 12 ++++++++++++
> tests/ref/fate/vsynth1-prores | 4 ++--
> tests/ref/fate/vsynth1-prores_kostya | 4 ++--
> tests/ref/fate/vsynth1-qtrle | 4 ++--
> tests/ref/fate/vsynth1-qtrlegray | 4 ++--
> tests/ref/fate/vsynth1-svq1 | 4 ++--
> tests/ref/fate/vsynth2-prores | 4 ++--
> tests/ref/fate/vsynth2-prores_kostya | 4 ++--
> tests/ref/fate/vsynth2-qtrle | 4 ++--
> tests/ref/fate/vsynth2-qtrlegray | 4 ++--
> tests/ref/fate/vsynth2-svq1 | 4 ++--
> 11 files changed, 32 insertions(+), 20 deletions(-)
>
> diff --git a/ffmpeg.c b/ffmpeg.c
> index 47a90da..81ee999 100644
> --- a/ffmpeg.c
> +++ b/ffmpeg.c
> @@ -846,6 +846,10 @@ static void do_video_out(AVFormatContext *s,
> method. */
> enc->coded_frame->interlaced_frame = in_picture->interlaced_frame;
> enc->coded_frame->top_field_first = in_picture->top_field_first;
> + if (enc->coded_frame->interlaced_frame)
> + enc->field_order = enc->coded_frame->top_field_first ? AV_FIELD_TB:AV_FIELD_BT;
> + else
> + enc->field_order = AV_FIELD_PROGRESSIVE;
> pkt.data = (uint8_t *)in_picture;
> pkt.size = sizeof(AVPicture);
> pkt.pts = av_rescale_q(in_picture->pts, enc->time_base, ost->st->time_base);
this does not look correct.
the field_order flag should be set before writing the header, its
just quicktime that uses it at trailer writing time
also we possibly need to clarify the distinction of semantic and
syntactic interlacing, content can be interlaced or not independant of
being coded as interlaced or not interlaced in the video bitstream.
I am not sure mov makes this distinction but others like h.264 do.
Its perfectly normal to have material flaged as progressive and
coded as interlaced frames. That is for example also one could use
ildct on progressive material and this should not turn the material
into interlaced.
video codecs that do not allow these 2 to be different can make use
of the semantic interlaceing information in their syntax. Which i
belive applies to some codecs in mov.
One question open is what does AVCodecContext.field_order represent
when the 2 are different. I think it should represent the semantic
interlacing because noone really cares if a bitmap was coded interlaced
its much more interresting if its content is interlaced in the sense
of even/odd lines being captured at diffrent times.
With this definition field_order would be similar to the aspect ratio
and passing it can then likely be done the same way
it would be needed to add a interlace / top_field_first to AVFilterLink
probably and pass the flags through avfilter and update in some
filters
or it will be needed to inject frames throgh avfilter before the
muxers write header is called to get this information.
For now iam surely also happy without this and just passing directly
when there are no filters and not at all if there are filters.
But maybe iam missing something and above is not the best solution?
> @@ -868,6 +872,14 @@ static void do_video_out(AVFormatContext *s,
> big_picture.top_field_first = !!ost->top_field_first;
> }
>
> + if (big_picture.interlaced_frame)
> + if (enc->codec->id == AV_CODEC_ID_MJPEG)
> + enc->field_order = big_picture.top_field_first ? AV_FIELD_TT:AV_FIELD_BB;
> + else
> + enc->field_order = big_picture.top_field_first ? AV_FIELD_TB:AV_FIELD_BT;
why the special case for mjpeg ?
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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